Body temperature is universally accepted as an important indicator of the physical condition of humans and other warm blooded animals. For many years, the most common method of measuring body temperature was to insert a contact type thermometer into the patient's mouth or rectum relying on conduction of heat to register an accurate temperature. One such thermometer is a mercury-in-glass thermometer. These thermometers are potentially hazardous due to a possibility of a mercury spill and glass breakage. An alternative contact type thermometer is an electronic “pencil” thermometer. These traditional thermometers will not register a body temperature until after they are left in the patient's mouth, rectum or other location for a relatively long time, thus making the measurement slow and uncomfortable.
A more advanced instrumentation has been developed for measuring the human body temperature by non-contact readings of the infrared (IR) emissions from the tympanic membrane and the ear canal. That is, the IR sensor element takes a reading without the sensor or associated sensing elements having to contact the patient. This technology has been the subject of patents to O'Hara et al. (U.S. Pat. No. 4,790,324) and Fraden (U.S. Pat. No. 4,854,730). The determination of body temperature from an IR reading of the ear drum or ear canal avoids a need of insertion of a probe into a mouth or rectum and allows a measurement of body temperature within a few seconds. However, the IR thermometers have their own problems, the most important of which is susceptibility to the operator's technique of taking a temperature. Other drawbacks include effects of ambient temperature and sensitivity to cleanliness of the IR lens. The IR thermometers are also relatively expensive.
Another IR thermometer, which is exemplified by U.S. Publication No. 2002/0114375 by Pompei, describes estimation of a core temperature by measuring the skin temperature and the ambient temperature by use of an IR emission detector. This method, however, suffers from other limitations, including an operator's technique, higher cost and other factors.
Any traditional contact (non-IR) thermometer has a probe with a temperature sensor that responds to temperature of an object, i.e., a thermal temperature sensor. The rate of response depends on the degree of a thermal coupling with the object, nature of an object, the sensor's isolation from other components and its thermal capacity. There are two known techniques in the art of a contact thermometry. One is the equilibrium and the other is the predictive technique. The equilibrium demands a sufficiently long time to allow the sensor to stabilize its response, meaning that the sensor's temperature and the object's temperature become nearly equal. The predictive technique is based on measuring the rate of the sensor's response and estimation of its would be equilibrium level which is not actually achieved during the measurement but rather anticipated mathematically. The latter technique allows a much quicker measurement but can result in some loss in accuracy. The predictive method is exemplified by U.S. Pat. No. 3,978,325. Some of the predictive techniques rely on a software data processing, while others rely on a hardware design. For instance, U.S. Pat. No. 3,872,726 issued to Kauffeld et al. teaches forecasting the ultimate temperature of a slow responding thermistor in a contact thermometer by using a hardware integrator. These thermometers are still intended for insertion into a body orifice.
It is therefore an object of the present invention to provide an electronic thermometer that can register a core body temperature of a mammal without necessarily being inserted in the mouth or rectum.
It is another object of the present invention to provide an electronic thermometer that can register a core or internal body temperature of a warm blooded animal or human patient quickly after contacting the patient's skin.
It is another object of the present invention to provide a thermometer that determines core body temperature in a manner that is less dependent on the operator's technique.
It is another object of the invention to provide an inexpensive thermometer which is easy to manufacture.
Further and additional objects are apparent from the following discussion of the present invention and the preferred embodiment.